1. Field of the Invention
The present invention relates to a device for elimination of hydrogen in burners or catalytic recombiners.
2. Background Information
The danger of hydrogen escape after occurrence of accidents exists in several power and process engineering plants. If oxygen is present, a combustible gas mixture capable of either turbulent deflagration or detonation can then be formed. The pressure wave generated by detonation can jeopardize or even destroy the components of a plant or the plant itself, as well as harm the surroundings.
Large quantities of hydrogen can be expected during serious accidents in, for example, water-cooled nuclear reactors (xe2x80x9cLWRxe2x80x9d) with non-inerted containments. In such reactors, failure of relevant safety systems and subsequent overheating of the reactor core lead to hydrogen formation by reaction of steam with the fuel cladding. In a large LWR, this process can release approximately up to 20,000 m3 of hydrogen at NTP into the containment in a few hours.
Preventive safety precautions comprise inerting the gas volumes with nitrogen, as is planned or already implemented in the case of boiling-water reactors. Catalytic recombiners represent countermeasures that have been discussed, and in some cases already installed. By means thereof, the hydrogen produced both inside and outside the ignition limits is recombined to steam by an exothermic catalytic reaction, thus generating heat. Hydrogen contents with concentrations inside the ignition limits can also be burned-off conventionally after external ignition.
For elimination of hydrogen from containments, both thermal and catalytic recombiners, which transform the hydrogen together with atmospheric oxygen into steam, have been developed. Preferred, however, are catalytic systems, which work passively, or in other words, without activation and without supply of electrical power, and therefore without heating and external energy for forced flow, since otherwise their availability could be jeopardized if the external energy supply were to fail. At present, there exist two concepts which have proved their feasibility in extensive tests, some with respect to potential catalyst poisons. Both metal foils and also highly porous granules, on which platinum or palladium is deposited as catalyst, are used as substrates. A plurality of foils and granule packages (in this connection the granules are held together by wire mesh and formed into packages) are disposed vertically and parallel to each other in sheet-metal housings. The hydrogen/air mixture enters the housing at the bottom. The reaction takes place at the catalyst-coated surfaces.
One disadvantage can be seen in the prior mixing in the large volumes of containments, so that a danger of explosions in containments exists. Ignition sources cannot be ruled out in such complex plants, especially after occurrence of serious accidents. Moreover, the oxygen and hydrogen reaction partners are fed to the recombiners in the form in which they are produced by mixing or in which they exist locally. Selective premixing or mixing before entry into the recombiners does not take place. The maximum decomposition rates and thermal efficiencies are limited by virtue of the flow over the catalytic surfaces and because of the limited convective heat removal. Moreover, the heat storage capacity is small. Excessive quantities of hydrogen can therefore lead to overheating of the coated substrates, so that the ignition limit is reached or exceeded, possibly also culminating as a result in homogeneous gas-phase reactions with deflagration or detonation.
Removal of the heat of reaction from the system is problematic in principle. It takes place almost exclusively by convection from the solid surfaces to the gases flowing past them, as well as by thermal radiation to adjacent structures. Because of the low overall height, upward flow inside the recombiner is slight. The flow is laminar and the heat transmission coefficient is therefore small. The additional heating of the surroundings must also be regarded as a disadvantage.
Furthermore, because of too low oxygen concentrations, high steam and hydrogen concentrations occur in conjunction with recombination, especially at high release rates.
The present invention is directed to solving the technical problem of reacting both large and also small quantities of hydrogen in a controlled manner in the immediate vicinity of the point of formation, while ensuring in particular an adequate oxygen supply for the reaction even of large quantities of hydrogen.
The technical problem described in the foregoing is solved according to the present invention by a device for elimination of hydrogen. According to the present invention, it has been recognized that in the very case of formation of large quantities of hydrogen, the oxygen needed for recombination must be drawn from the other zones of the containment and selectively fed to the device for reacting hydrogen and oxygen. For this purpose, pressure differences between the point of production of the hydrogen and the other zones of the containment, as well as energy present in the atmosphere, are used to drive machines with which, for example, the atmospheric oxygen needed for elimination is imported and injected together with the hydrogen into the device for reacting hydrogen and oxygen. Thus the quantities of hydrogen entering into the containments can be depleted to the extent that they lie under the ignition limit and that the danger potential is reduced therewith. Furthermore, the heat of reaction produced during elimination is used to drive the machines and is removed if necessary by means of coolers, so that the containment atmospheres are not additionally heated. The device according to the invention is therefore usable, by means of turbine processes, for example, over a large throughput range, since the quantities of hydrogen and steam, which are released in greatly varying rates depending on an accident scenario, can be reacted.
The present invention concerns a device for elimination of hydrogen comprising:
(a) a reactor for reacting hydrogen and oxygen, the reactor being provided with a first inlet line, a second inlet line and an outlet line, wherein the first inlet line admits a hydrogen-containing gas mixture into the reactor and the second inlet line admits a compressed oxygen-containing gas mixture into the reactor, the outlet line discharges a resultant gas mixture from the reactor after at least a partial reaction of the hydrogen and oxygen in the reactor,
(b) a turbine connected to a shaft which rotates with the turbine, and
(c) a compressor connected to the shaft so that the shaft transmits rotational movement generated by the turbine to the compressor, the compressor receives an oxygen-containing gas mixture and provides the compressed oxygen-containing gas mixture, the compressor being joined by a conduit to the second inlet line to pass the compressed oxygen-containing gas mixture into the reactor.
Since the turbine receives its drive energy from the operating atmosphere, it meets the criteria of passive or, in other words, self-activated safety systems.
Preferably the turbine is disposed upstream from the device for reacting hydrogen and oxygen, and is joined to the inlet line. Thus the turbine is located on the inlet side and is forced to rotate by the incoming gas mixture.
It is also possible to dispose the turbine downstream from the device for reacting hydrogen and oxygen and to connect it with the outlet line. In this case, the gas mixture formed after reaction of the hydrogen is used to drive the turbine. The latter arrangement is advantageous in particular if a second compressor is disposed upstream from the device for reacting hydrogen and oxygen and is joined to the inlet line. In this case, the hydrogen-containing gas mixture flowing into the second compressor is first compressed before being injected into the device for reacting hydrogen and oxygen.
Both a burner and a recombiner can be used as the device for reacting hydrogen and oxygen.
Furthermore, the first and/or the second compressor is advantageously designed as a turbine compressor, so that the large gas streams occurring during accidents can be dealt with by the device according to the invention, by virtue of the high gas throughput rates possible with turbine compressors. In particular, a quantity of air or gas mixture which depends on gas throughput and the speed of the turbine units is fed in this way to the device for reacting hydrogen and oxygen. However, the compressors can also be designed, for example, as piston compressors, as atmospheric steam engines or as Stirling engines.
Furthermore, it has been recognized that the aforementioned problem is also solved by a device for reacting hydrogen and oxygen which is designed as a burner or recombiner and which is disposed under a water surface. By virtue of this inherently independent inventive solution of the aforementioned problem, the large thermal energy generated in the burner or recombiner is removed in the most optimum manner possible, by the fact in particular that full-surface contact with a water volume is achieved.
The aforementioned components to be used according to the present invention, which are also described in the practical examples, are not subject to any particular exceptional conditions as regards their size, geometry, material selection and technical concept, and so the selection criteria known in the area of application can be applied without restriction.